In a four-stroke cycle engine, a lubricant as engine oil is stored in a bottom of a crankcase. The lubricant is supplied to appropriate sliding portions that require lubrication, such as a bearing portion of a crankshaft incorporated in the crankcase, a joint portion between the crankshaft and a connecting rod, and a portion between a piston and cylinder bore. In a utility engine used as a power source for a generator or atomizer, the lubricant stored in the bottom of the crankcase is splashed to the sliding portion by a scraper formed on the connecting rod.
On the other hand, a slant engine is used as the power source of the generator etc. As for the slant engine, the cylinder is assembled to the crankcase in such a way that a cylinder bore axis line (a central axis of reciprocation piston) is slanted toward a rotational direction of the crankshaft.
When the slant engine is viewed from a direction along the crankshaft, the cylinder is as assembled to one side of the crankcase. The scraper in the slant engine is assembled at the end portion of the connecting rod so as to splash the lubricant toward an inner surface of the crankcase.
As for such slant engine, if the engine stands on a slope, the stored lubricant stays in one wall side of the crankcase. Thus, when the slant engine is used in the foregoing condition, the scraper may be unable to reach to a liquid surface of the lubricant otherwise it may sink deeply into the lubricant so that it cannot work appropriately for the lubrication in the crankcase.
Japanese Utility Model Laid-Open No. 5-50012 discloses the slant engine comprising partition boards in an oil pan of the crankcase and an oil strainer provided between partition boards so as to prevent accidental entry of air bubbles into the oil strainer by fluctuation of the liquid level.
On the other hand, Japanese Patent Laid-Open No. 11-81966 discloses an engine, but not the slant engine, having an upright cylinder. This engine has an outside reservoir oil tank in addition to the oil pan of the crankcase and a solenoid valve provided in an oil passage connecting the oil pan and the reservoir oil tank for controlling the “open/close” states of the oil passage, so as to increase quantity of lubricant without upsizing the crankcase,
It is preferred to increase quantity of lubricant to extend a maintenance period of the lubricant. Where the oil strainer are provided between the partition boards as shown in Japanese Utility Model Laid-Open No 5-50012, it is difficult to increase the quantity of lubricant although the lubricant can be supplied to appropriate portions even if the slant engine stands on a slope.
Furthermore, when the reservoir oil tank is formed outside the crankcase and the solenoid valve controls the passage to the reservoir oil tank depending on a signal from the sensor detecting the level of lubricant surface of the oil pan as shown in Japanese Patent Laid-Open No 11-81966, the structure becomes complicate and the production cost becomes high. Furthermore, it is difficult to apply this structure to the slant engine.